Whisk together the flour, cocoa, baking soda, and salt in a bowl until combined.
Stir together the buttermilk and vanilla in a small bowl.
Beat together the butter and brown sugar in a large bowl with an electric mixer at medium-high speed until pale and fluffy, about 3 minutes in a standing mixer or 5 minutes with a handheld.
Add the egg, beating until combined well.
Reduce the speed to low and alternately mix in the flour mixture and the buttermilk in batches, beginning and ending with the flour, scraping down the sides of the bowl occasionally, and mixing until smooth.
Spoon 1/8-cup mounds of batter about 2 inches apart onto large buttered baking sheets.
Bake in the upper and lower thirds of the oven, switching the position of the sheets halfway through baking, until the tops are puffed and the cakes spring back when touched, 8 to 11 minutes.
Transfer the cakes with a metal spatula to a rack to cool completely.
Beat together the butter, confectioners’ sugar, marshmallow, and vanilla in a bowl with electric mixer at a medium speed until smooth, about 3 minutes.
Spread a rounded ½ tablespoon of filling on the flat sides of half of cakes and top with the remaining cakes.
September 29, 2008
Made these with sweetened whipped cream instead of the marshmallow in the recipe above. Everyone liked them, but they were too big, so I altered the recipe above to be half the size (the recipe originally made eight big pies). Very easy to make. I lined the baking pans with parchment paper. Gourmet/ January 2003